Update the Babel plugin to remove empty static initialization blocks

[Snuffleupagus]

We have static initialization blocks that include pre-processor statements which make them conditionally empty, note e.g. how the following source code:

pdf.js/src/display/api.js

Lines 2016 to 2054 in c60c0d1

	static {
	if (typeof PDFJSDev === "undefined" || PDFJSDev.test("GENERIC")) {
	if (isNodeJS) {
	// Workers aren't supported in Node.js, force-disabling them there.
	this.#isWorkerDisabled = true;
	GlobalWorkerOptions.workerSrc ||= PDFJSDev.test("LIB")
	? "../pdf.worker.js"
	: "./pdf.worker.mjs";
	}
	// Check if URLs have the same origin. For non-HTTP based URLs, returns
	// false.
	this._isSameOrigin = (baseUrl, otherUrl) => {
	let base;
	try {
	base = new URL(baseUrl);
	if (!base.origin || base.origin === "null") {
	return false; // non-HTTP url
	}
	} catch {
	return false;
	}
	const other = new URL(otherUrl, base);
	return base.origin === other.origin;
	};
	this._createCDNWrapper = url => {
	// We will rely on blob URL's property to specify origin.
	// We want this function to fail in case if createObjectURL or Blob do
	// not exist or fail for some reason -- our Worker creation will fail
	// anyway.
	const wrapper = `await import("${url}");`;
	return URL.createObjectURL(
	new Blob([wrapper], { type: "text/javascript" })
	);
	};
	}
	}

is transformed into (in that case for the MOZCENTRAL build):
https://searchfox.org/mozilla-central/rev/b6671f4c3afdb2b36e63c9d176f98a5959907259/toolkit/components/pdfjs/content/build/pdf.mjs#10434

Hence it seems like a good idea to, if possible, extend the Babel plugin to remove static initialization blocks that become empty during building.

[nicolo-ribaudo]

I'll take a look